Process for purifying metals



I April 21, 1942. T. R. JONES PROCESS FOR PURIFYING METALS Filed March 20, 1941 INVENTQR OMAS R, J NE BY ATTQRNEYS Patented Apr. 21, 1942 I UNITED STATES PATENT OFFICE 2,280,706 PROCESS FOR PUBIFYING METALS Thomas B. Jones, Woodbridge, N. L, asslgnor to The American Metal Company, Limited, New York. N. Y, a corporation of New York Application March 20. 1941, Serial No. 384,260

12 Claims. (CI. 75-85) My invention relates to aprocess of removing} lead from tin and is especially useiul in removing small amounts of lead irom otherwise pure. tin. My invention has further reference to an; paratus tor periorming the described process and such other metal-separating processes as tion of the products may he attempted. It is evident that this type oi process requires elaborate apparatus and, due to the corrosiveness oi the products, presents a serious and difilcult problem in construction and operation. There have been many other methods and apparatus proposed for the separation oils and tin by means of chlorine and chlorides, but none have had the simplicity, practicability and novelty of my invention. 7

I have devised a process and apparatus in which a bath of molten tin containingsome lead may be reduced in lead content to less than 0.05 percent. The lead is recovered as a retort residue by distilling SnCh away from a SnClz-PbCh mixture and returning the lead-free SnClz to a tin de-leading kettle.

The removal oi lead' from tin'by means of chlorine depends upon the greater aiilnity of chlorine for lead than for tin. It a lead-tin alloy is treated with a given amount of chlorine, a PbClz-SnCl: dross forms on the metal, in which the lead-tin ratio eventually comes to a definite figure depending on the final lead-tin ratio or the alloy upon which the dross rests.

The reaction Pb+SnClr+PbCh+Sn is reversi-- it Such is continually added to the lead-tin,

leadchloride, stannous-chloride system shown above, the reaction will go from leit to right, and that it the PbCl: is continuously removed from the system, theneventually substantially all of the lead will be removed from the tin.

In order to do this, I remove PbClz-SnClr adjacent the retort I0.

dross from the metal bath continuously and place it in a retort where the dress is raised in temperature in order to distill of! the SnClz which is returned to the metal bath whereiit reacts with the lead of the metal bath to form PbClz and metallic tin according to the above mentioned equation, thereby repressing the formation of more SnCl; and accelerating the formation of PbCla. By this procedure, the PbCla continuously accumulates in the retort, whereas the SnCh is continually circulating and being drawn of! to the retort with some lead. In this way, practically all the lead may be removed irom the tin. 7

On the accompanying drawing:

Figure 1 is a vertical sectional view, partly in elevation, showing one form of apparatus suitable for practicing the invention; and

Fig. 2 is a plan view, partly in section, of the apparatus shown in Fig. 1.

As shown on the drawing, l represents a deleading kettle which is mounted on a suitable support 2, The kettle I is closed by a cover plate 3 suitably anchored in closing position. An electrical motor 4 carried by a suitable support 5 operates a depending, vertical shaft 6 which extends downwardly thru the cover plate I and, at its lower end, carries an agitator 'l.

Suitably secured to the interior surface of the kettle I is an angular member 8 which forms a chamber or dross trap open at its upper and lower sides. The kettle l is provided with an opening la which places the dross trap in communication with an inclined conduit 9 adapted to discharge into a suitably supported retort ill closed by a cover plate ll. Adjacent its upper end, the retort in bass. second inclined conduit l2 communicating therewith, said conduit l2 extending toward and opening into a vertical pipe l3 adapted to discharge into the kettle 1 thru an opening 3a provided in the cover plate I, the pipe l3 being closed by 'a detachable plug ll.

In accordance with the invention, the cover plate I may carry a funnel l5 adapted to be closed or sealed by a slide'plate Hi. In addition, said cover plate 3' may carrya pipe l1 adapted to be closedby a valve is. As indicated, the funnel II and the pipe I! communicate with kettle thru openings provided, respectively,'therefor in the cover plate 3.

Further, as shown, a suitable heating device I. should be associated with the kettle I and,

similarly, a heating device 20 should be disposed After a suitable quantity of melted lead-containing tin has been pumped or otherwise suitably passed into the kettle I, the operation proceeds in the following manner. Iinitially, it :Is necessary to provide a cover or upper layer of SnCli on the melted lead-containing tin and this may be accomplished in any one of a variety of ways. Thus, 9. Such dross may be introduced into the kettle I by passage thereof thru the funnel I5 after the slide plate I6 has been opened, the latter being closed after the desired. amount of SnCl: dross has been passed into said kettle I. Alternatively, in order to chlorinate some of the tin, chlorine gas may be passed into the kettle Iby way of the valvecontrolled pipe II. In lieu of the foregoing, S'nClz vapor may be passed into the kettle I from the retort I II which, as hereinafter described, constitutes a source of supply of such .-in the dross trap formed by the member 8 from which the collected dross flows thru the pipe 9 and passes into the retort I0, this operation proceeding in a continuous manner as will be understood.

While the foregoing'operation proceeds, the burner 20 should be operated to maintain the material in the retort III at a temperature ranging between 1200 degrees F. and. 1300 degrees F. This causes the S1101: to distill away from the lead chloride and return, by way of the conduit II, to the kettle I and again enter into reaction with the metallic lead therein so as to form additional lead chloride which,.in turn, as a dross passes to the retort III to continue the process. In this, connection, it will be understood that the vapor pressure in the retort I0 becomes sufllciently high to pass SnClz vapor from .sald re tort ID to the kettle I byway of the conduit I2,

condensing in saidconduit or kettle.

'Eventually, in the manner described, substantially all of the lead is removed from the tin in the kettle I, the lead thus'removed'remaining in the retort III as will be understood. As the proc ess nears its conclusion, the temperature of the material in said retort III may be increased as high as 1500 degrees F., this high temperature being utilized in order to drive off as much-311C112 I from the retort I0 as possible while not bringing the temperature sufllcientlyhigh to vaporize lead chloride. This assures the highest possible lead content of the lead residue remaining in the retort III. This lead'residue is removed from the retort III from,time to time depending on the amount of lead "present in the original tin charged into the kettle I. The stannous chloride is melted to recover the tin.

I have found that an ordinary iron retort l0, when used in performing the described process, does not last very long due to the corrosive action of PbCl: and SnClz. Special alloys or a metal such as copper orthe like are necessary in commercial practice. I have .found that "Hastelloy B withstands the corrosive. action very well.

While the invention has been described in de- I vention, that changes and modifications may be made therein without departing from the spirit or scope of the invention, and it is intended in the appended claims to cover all such changes and modifications.

What is claimed as newand desired to be secured by Letters Patent, is:

1. The process of removing lead as an impurity from tin, which comprises forming a dross of stannous chloride andlead chloride on a mass of molten tin containing the lead impurity. passing the dross away from the molten tin and separating the stannous chloride from the lead chloride.

2. The process of removing lead as an impurity from tin, which comprises forming a dross of stannous chloride and lead chloride on a mass of molten tin containing the lead impurity, passing the dross to a retort, maintaining the retort temperature sufllciently high to cause the stannous chloride to distill from the lead chloride, and returning the stannous chloride to the zone occupied by said mass of molten tin.

3. The process of removing lead as an impurity from tin, which comprises forming a dross of stannous chloride and lead chloride on a mass of molten tin containing the lead impurity, trapping the dross and passing the same to a retort under the action of gravity, maintaining the retort temperature sufldciently high tocause the stannous chloride to distill from the lead chloride, and, responsive to the pressure existing in said retort, returning the stannous chloride to,

the zone occupied by said mass of molten tin.

4. The process of removing lead as an impurity from tin, which comprises melting the tin having the lead impurity therein, producing'a layer of stannous chloride on the surface of the molten metal. agitating the molten metal to cause the stannous chloride to react with the lead and thereby produce a dross of stannous chloride and lead chloride, elevating the temperature of the dross after removal thereof from the melting zone to distill the stannous chloride from the lead chloride, and returning the stannous chloride'to,

the melting zone.

5. The process of removing lead as an impurity from tin, which comprises melting the tin having the lead impurity therein, producing a layer of stannous chloride on the surface of the molten metal, agitating the molten metal to cause the stannous chloride to react with the lead and thereby produce a dross of stannous chloride and lead chloride, passing the dross to a zone wherein the stannous chloride is separated from the lead chloride, and returning the stannous chloride to I the melting zone.

6. The process of removing lead as an impurity from tin, which comprises melting the tin having the lead impurity therein, producing 'a layer of stannous chloride on the surface of the molten metal, agitating the molten metal to cause the stannous chloride to react with the lead and thereby produce a dross of stannous chloride and lead chloride, trapping the dross and passing the same to a retort under the action of gravity, maintaining the retort temperature sufllclently high to cause the stannous chloride to distill from the lead chloride, and returning the stannous chloride to the melting zone.

7. The process of removing lead as an impurity from tin, which comprises melting the tin having the lead impurity therein, producing a layer o! stannous chloride on the suriace oi the molten metal, agitating the molten metal, while maintaining the temperature thereof between 470 degrees F. and .600 degrees F., to cause the stannous chloride to react with thelead and thereby produce a dross of stannous chloride and lead chloride, passing the dross to a retort, maintaining the retort temperature between 1200 degrees I". and 1300 degrees F. to cause the stannous chloride to distill from the lead chloride, and retum ing the stannous chloride to the melting zone.

8. The process 01' removing lead as an impurity from tin, which comprises melting the tin having the lead impurity therein, producing a layer of stannous chloride on the surface of the molten metal, agitating the molten metal, while maintaining the temperature thereof between 470 degrees F. and 600 degrees F., to cause the stannous chloride to react with the lead and thereby produce a dross of stannous chloride and lead chloride, passing the dross to a retort, maintaining the retort temperature between 1200 degrees F. and 1300 degrees F. to cause the stannous chloride to distill from the lead chloride, and, when the tin in the melting zone becomes substantially tree from lead, elevating the retort temperature to 1500 degrees F. approximately.

9. In the art or removing lead as an impurity from tin, ,the steps which consist in continuously passing a dross oi stannous chloride and lead chloride from a kettle to a retort, distilling the stannous chloride from the lead chloride in the retort, and continuously passing the stannous chloride vapor from the retort to the kettle.

10. In the art of removing lead as an impurity from tin, the steps which consist in continuously passing a dross 0t stannous chloride and lead chloride to a retort from a kettle containing the tin and the lead impurity in molten condition, distilling the stannous chloride from the lead chloride in the retort, continuously passing the stannous chloride vapor from the retort to the kettle, and agitating the molten metal in the kettle to cause the stannous chloride to react with the lead and thereby produce a further dross supply oi stannous chloride and lead chloride.

11. In the art of removing lead as an impurity from tin, the steps which consist in continuously passing a dross of stannous chloride and lead chloride to a retort from a kettle containing the tin and the lead impurity in molten condition, maintaining the retort temperature between 1200 degrees F. and 1300 degrees F. to cause the stannous chloride to distill from the lead chloride, continuously passing the stannous chloride vapor from the retort to the kettle, and agitating the molten metal in the kettle, while maintaining the temperature thereof approximately between 470 degrees F. and 600 degrees F., to cause the stannous chloride to react with the lead and thereby produce a further dross supply of stannous chloride and lead chloride.

12. In the art of removing lead as an impurity from tin, the steps which consist in continuously passing a dross ot,stannous chloride and lead chloride to a retort from a kettle containing the I tin and the lead impurity in molten condition,

lead and thereby produce a further dross supply of stannous chloride and lead chloride.

THOMAS R. JONES. 

